Semidiurnal tide in the 80–150 km region: an assimilative data analysis

Abstract

A set of tabulated functions called 'Hough Mode Extensions' (NM&), which represent numerical extensions of classical Hough modes into the viscous regime of the thermosphere, are used to leastsquares fit a climatological data base of tidal measurements. The data base consists of monthly average vertical profiles of semidiurnal amplitudes and phases at I7 radar sites accessing some part of the 80-I 50 km height region. The radars are distributed between 78 S and 70 N latrtude, and each one provides measurements of one or more of the following: eastward wind, southward wind, perturbation temperature. As a result of the fitting process. a single complex normalizing coefficient is derived for each month and for each of the four HMEs, designated (2,2), (?,3). (2.4) and (2.5) after their classical Hough function designatioI]s. Once the complex coefficients are derived, re~onstru~lion by weighted superposition of the HMEs results in globally continuous specifications of semidiurnal horizontal and vertical wind, temperature. pressure, and density throughout the X0-150 km height region. The tidal variations in density. in particular, provide greater accuracy for several aerospace applications. The methodology developed here can also be utilized to derive tidal lower boundary conditions for Thermospheric General Circulation Models (TGCMs), or as a basis for future empirical model development. Comparisons are also made with HME coefficients and global tidal field5 from the F~KHES and VIAL [(IY89) J. NII~MJS. /err. Ph~~s. St, 6491 numerical tidal model.

Comment on "Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)" by Pancheva et al. (2009)

“…Also, Hough mode extensions (HME; e.g. Forbes et al, 1994) have been used to provide tidal perturbations for winds, temperatures and densities at other heights and latitudes when the amplitude and phase of the wind field for a given HME is known for one height and latitude. Forbes and Wu (2006) showed the convincing consistency of the global temperature-structure at 86 km for the diurnal tide's NMT (s=−3) as observed by MLS (Micro-wave Limb Scanner, UARS), and the temperatures derived from HME using the observed winds at 95 km from UARS (Upper Atmosphere Research Satellite), WINDII (Wind Imaging Interferometer) and HRDI (High Resolution Doppler Interferometer).…”

“…Remote sensing instruments on board satellites have made possible the delineation of nearly global distributions of tides. From HRDI-UARS wind observations, Manson et al (2002c) obtained the global distributions of D and SD tides at ∼96 km for June-July (1993), December-January (1993/1994 and September-October (1994). The SDT-wind maximized near 40-55 degrees in winter and fall, and exhibited more modest longitudinal amplitude variations than the DT-wind.…”

Studies of the E-Region Neutral Wind in the Auroral Ionosphere Using Two Long-Run Data.

“…4.4.2 The March experiment Forbes and Vial (1991) have shown global features of the semidiurnal zonal amplitude for March using the Hough mode extension technique (see Forbes and Vial, 1989 and references therein). From the Fig.…”

“…From the Fig. 1(a) of Forbes and Vial (1991), the semidiurnal zonal amplitude at 70°N at heights of 101, 108, and 119 km are determined to be about 25, 57 and 50 m s-1, respectively. The corresponding amplitudes derived for the March experiment are about 15, 26, 34 m s-1 obtained by FFTO, and about 16, 21, 37 m s-1 obtained by LSF.…”

Sensitivity studies of the E region neutral response to the postmidnight diffuse aurora

“…Several studies have generated climatologies for the amplitudes and phases of propagating tides in the thermosphere (e.g. Manson et al, 2002;Forbes et al, 1994;Forbes and Vial, 1991), but propagating tides show great day to day variability in amplitude and phase (e.g. Pancheva et al, 2000;Beard et al, 1999;Canziani, 1994;Phillips and Briggs, 1991), so the amplitude and phase of the tides for a specific day and location is not well known, in the absence of direct measurements.…”